Commit rGHC8b007ab assigns the same label to the first basic block
of a proc and to the proc entry point. This violates the PPC 64-bit ELF
v. 1.9 and v. 2.0 ABIs and leads to duplicate symbols.
This patch fixes duplicate symbols caused by block labels
In commit rGHCd7b8da1 an info table label is generated from a block id.
Getting the entry label from that info label leads to an undefined
symbol because a suffix "_entry" that is not present in the block label.
To fix that issue add a new info table label flavour for labels
derived from block ids. Converting such a label with toEntryLabel
produces the original block label.
Fixes Trac #14311